"It was all a bit like a series of blind dates to see how we hit it off. It took us a couple of sessions before we found out what the best method was. The chemistry felt really good all throughout the process," Epworth said.
"We went on a couple of dates," said band leader Marcus Mumford. "We did sessions before Christmas, which led to pretty much the final version of the song called 'Slip Away,' which is on the record. And we just felt like he was exactly the person we needed to help steer this ship for this fourth record. And we've never enjoyed recording more."
The result is the 14-track "Delta," to be released Friday. The band started writing new music after the album "Wilder Mind" was released in 2015, even though one of the "Delta" songs is six years old. Mumford said they tried to re-work the old track "about 400 times."
"It's called 'Forever' — ironically," he said. "It wasn't called 'Forever' before. After the 600th time," chimed in Winston Marshall, who plays banjo and electric guitar. Epworth was part of the solution. The band says when they didn't know what to do, he did.
"They were open to giving me a bit of space to run with stuff (and) try out what I had in mind," Epworth said. "It definitely made me feel like I was essentially a fifth member of the band." The London group said they were familiar with Epworth's work — the producer is best known for crafting Adele's monster hit "Rolling in the Deep" and also winning an Oscar with the British vocalist for the James Bond theme song, "Skyfall." Epworth's credits also include songs with Coldplay, Florence + the Machine, U2, and Foster the People as well as lesser known acts such as Glass Animals, Bloc Party and Plan B.
Markus Dravs produced the band's 2009 debut, "Sigh No More," and its follow-up, 2012's "Babel," which won the album of the year Grammy. Both records reached multi-platinum status and launched hits on the pop and rock charts. "Wilder Mind," produced by James Ford, still had rock hits but only went gold.
Epworth's fifth member status proved invaluable for "Delta," mainly recorded at Epworth's The Church Studios in London. "(Paul) would just come back one day and be like, 'That is not your upbeat rock song. That is your downbeat piano ballad. We'd be kind of just blindsided by the moments of sheer visionary," said multi-instrumentalist Ben Lovett.
"Especially for a band of four collaborators — to have that person to help, decision-tie-breaker, those sort of moments (are important)," Lovett added. "If it were to be that we kind of fell out with our producer, it would be fine because we could leave the situation. If we fall out with each other, we've got a major problem. Luckily that's been something we've been able to avoid."
The songwriting process for each track on "Delta" varied — each of the band members work on songs individually and then bring them to the group. Mumford said over the years he's learned how to be a better team player and let everyone's voice be heard.
"In the old days there was a sliver of immediacy and I think a slight immaturity, creatively. ... If someone else had a different idea, I personally had less patience for it than I do now," he said. "Now, I trust these guys' creative instincts so much. If they've got a different idea (and) it doesn't chime with me straight away, I'm intrigued to see where it goes."
One of the ideas that came from Lovett was "If I Say," a beautiful, building rock song, where the string arrangement and orchestra shine brightly. Lovett said he wrote the song "in a dream that I had whilst I was going through a bunch of stuff."
"I was halfway between grappling with a divorce but also being in a new relationship," he continued. "The song questions a lot about commitment and about the power of commitment." Personal experiences are what drove the overall songwriting behind the album, bassist Ted Dwane said.
"We write autobiographically. A lot has happened to us in our personal lives in the past few years and the overriding theme felt like entering the world," Dwane explained. "It felt like leaving the security of youth and innocence and manning up, basically."
Mumford & Sons, who formed in 2007 and started out as a live band, will get a chance to showcase the new songs on their 60-date "Delta" Tour, which kicks off in Dublin on Friday and lands in the U.S. on Dec. 7 in Philadelphia.
They said another way they were inspired to write new songs came from listening to other artists' music in the studio. "We'll constantly be introducing each other to new music like, 'Listen to this song here' and we'll turn it up loud," Mumford said. "Wins and I once had a very late, quite drunken night in London, demoing for the previous album where we listened to (Don Henley's) 'The Boys of Summer' about five times really loud and then tried to record our own. We called it 'Lads of Summer.' It's a monstrosity. We should have put it on the record though."
"Maybe on the next one," Marshall said. "By the way, I (expletive) love that song."